Delivery of data packets from multimedia sources over wide area networks (WAN), such as cellular networks, is often plagued with a high packet loss rate caused by wireless link failures resulting from shadowing, fading and interferences. For point-to-point unicast delivery, sophisticated schemes using combinations of automatic retransmission request (ARQ) and forward error correction (FEC) schemes are deployed at the Application, Radio Link Control (RLC), MAC and Physical layers to combat packet losses. These schemes rely on a fast and reliable feedback channel from the receiver to the sender at the multimedia sources or base stations to report statuses of transmitted packets. Typically, the resulting throughput is lower or additional network resources are required to maintain the same throughput when the channel conditions a user experiences is poor.
Multimedia sources employing Multimedia Broadcast Multicast Service (MBMS), which is a broadcast/multicast service specified in the 3rd Generation Partnership Project (3GPP), use a single transmission channel for broadcast or multicast to multiple users demanding the same content. Although the multicast mode of MBMS has an available feedback channel, the well known NAK implosion problem, in which the single sender is overwhelmed by the number of ARQ requests from a large number of receivers, means that many of the ARQ-based or hybrid ARQ/FEC transmission mechanisms developed for point-to-point unicast transmissions cannot be deployed for MBMS when the receiver group is large. As a result, the common transport strategy for MBMS is forward error correction (FEC)-based, where FEC codes like the Raptor Code is applied at the application layer to improve video streaming quality. FEC-based schemes for MBMS are usually optimized for the average user. As such, at any given time, unlucky users experiencing worse-than-average channel conditions will suffer significant packet losses. Mathematically, the typical MBMS media distribution optimization for the average user is of the form:min Davg(Rs,Rc)s.t. Rs+Rc≦C  Equation (1):
In Equation (1), the sender attempts to minimize the distortion of the average user Davg using source bits Rs to encode the media source and channel bits Rc to protect the encoded source bits (using FEC, for example) subject to a channel bitrate constraint C. If, on the other hand, FEC-based schemes for MBMS are optimized for the worst user at any given time, then significantly more channel bits Rc are needed to combat more frequent channel losses of the worst channel, meaning there are fewer bits leftover for source bits Rs to encode the media source, which often leads to a poor visual quality for everyone in the multicast group.
An improved approach to reducing or eliminating packet losses incurred during a multicast or a broadcast to a group of receivers without substantially increasing throughput requirements would therefore be beneficial.